Apparatus, system, and method for low cost high resolution chemical detection

ABSTRACT

An apparatus, system, and method are disclosed for low cost high resolution chemical detection. The apparatus includes two outer sealing bodies with flow channels etched into the bodies. Two gas chromatography (GC) columns are between the outer bodies, with a valve that switches flow regimes from series flow through the two GC columns to sample flowing directly to each GC column. The flow regimes are achieved with a single pump or dual pumps, and with one to three flow restrictions. The apparatus includes a preconcentration tube for concentrating chemicals of interest from the sample, and a sample switching valve and sampling pump to switch the sample flow from concentrating sample to delivering concentrated sample. The apparatus includes an engineered leak to equalize flow between a sample channel and a detector circuit. The sample channels may have impermeable inserts allowing the apparatus to measure chemicals in the parts-per-billion range.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims benefit of U.S. patent application Ser. No.60/805,309 entitled “APPARATUS, SYSTEM, AND METHOD FOR BROAD SPECTRUMCHEMICAL DETECTION” and filed on Jun. 20, 2006 for Arnold et al., whichis incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to chemical detectors and more particularlyrelates to gas chromatography sensors.

2. Description of the Related Art

Gas chromatography (GC) is useful in the chemical industry as aseparation mechanism and as a sensing mechanism. GC sensors areextremely useful for detecting specific chemicals in a gas with mixedcomponents, but they suffer from the major drawback that they are quiteexpensive.

The required purities in GC mandate, within most of the current art, theuse of valves that cost in the thousands of dollars per valve. Oneconcept has been introduced which allows air pressure to perform some ofthe gas switching, which allows the expensive valves to be replaced withcheaper solenoid valves, see U.S. Pat. No. 4,970,905. However, thepresent art for accomplishing this requires complicated machining andassembly causing manufacturing expense and reliability problems.

Another limitation of the present art is that manufacture of GC columnsis a tedious and expensive process. For example, the GC column must beheated uniformly while in use, and low cost methods to effectivelyaccomplish this uniform heating are lacking in the present art. Onecurrent method to provide effective and affordable heating is toco-axially winding a heating element around the GC column—this method isexpensive to implement. There are temperature control methods which areeasy to manufacture, but which tend to leave the GC column directlyexposed to a heating element and thus allow for non-uniform temperaturespikes at places along the GC column.

Another limitation of current GC sensor technology is that the sensorsneed to be periodically calibrated against an internal standard, and nocheap methods exist to provide for this. The current technology is toprovide a chemical, which must be stored, and an injection mechanismwhich must inject the chemical into the system without interfering withseals and the normal operation of the GC sensor.

GC sensors typically use a preconcentration mechanism, which multipliesthe concentration of chemicals of interest in a sample and allowsdetection of lower initial concentrations than otherwise allowable.Typically, an absorption-desorption material is added into the samplestream to accomplish this. Current methods of addingadsorption-desorption materials tend to cause variable pressure drop inthe sensor flow paths.

In the current art, the GC sensor must operate at a design operationaltemperature. Lower temperatures are desirable for better separation ofelution times of different components, while higher temperatures improvethe sensor response time. However, the test temperature must be at leastas high as the ambient temperature. Typically, an operating temperatureis selected that is higher than any predicted ambient temperature whenthe GC sensor is manufactured. This causes the temperature to be sethigher than necessary when the actual ambient temperature is low, makingchemical detection more difficult than required, and inducing greaterenergy loss to heat the GC sensor than would otherwise be required.

In GC sensors that detect a wide range of chemicals, the chemicals canhave widely variable elution times from the GC column. Further, theshape of the detection peaks for chemicals with different elution timeswill vary. As a general principle, later eluting chemicals will have alower and wider peak than early eluting chemicals. Further, in highresolution GC sensors that are detecting concentrations in theparts-per-million (ppm) and parts-per-billion (ppb) ranges, extraneouspeaks and noise will occur in the basic signal. This variability in peakshape makes it difficult for detection algorithms to correlate theconcentrations of the various chemicals.

A GC sensor will typically have a long GC column placed into a smallarea, and will typically be wound up as tight as possible. Further, theGC column may be manufactured in one time and location, and transportedand/or stored for a period before assembly of the GC sensor. A cheapmethod to build uniform GC columns, and to protect the columns from theintroduction of impurities between the time of manufacture and the timeof assembly is desirable.

A dual hyphenated GC sensor, and any GC sensor that is either utilizedto detect many chemicals simultaneously, or utilized to detect chemicalsfrom a complex mixture of gases, suffers in the current art fromdifficulty in finding chemical elution peaks within a complex signal.Often a significant amount of noise is produced in the signal. Thestandard Fourier analysis of GC signals suffer from producing ringing inthe signal, especially with high frequency components of the signal.Noise suppression wavelets are known in the art, but any particularnoise suppression wavelet will still tend to leave some noise peaks inthe signal and complex signals continue to be difficult to interpret.

Proper sealing of GC sensors is a known difficulty in the art, and isespecially problematic in sensors attempting to detect chemicals at thelow parts-per-million (ppm), or even into the parts-per-billion (ppb)range. The internal flowpaths of the sensor must be protected fromleakage to the ambient environment, and the analytical flowpathscontaining the chemical sample must be further protected fromun-designed fluid migration within the sensor.

From the foregoing discussion, it should be apparent that a need existsfor an apparatus, system, and method that detects a broad spectrum ofchemicals in a GC sensor in an inexpensive and effective manner.Beneficially, such an apparatus, system, and method would allow the useof inexpensive solenoid valves, provide for easy manufacture, providefor uniform and inexpensive heating of sensing elements, allow for a lowcost implementation of an internal chemical standard, provide formanufacture of a preconcentration system that is inexpensive andprovides uniform pressure drop, allows low energy operation in a widerange of ambient environments, that robustly detects chemicals that havewidely varying elution times, and that is protected from leakage fromthe ambient environment and internally within the analytical flowpaths.

SUMMARY OF THE INVENTION

Based on the foregoing, Applicant asserts that a need exists for a lowcost high resolution chemical detector. The present invention has beendeveloped in response to the present state of the art, and inparticular, in response to the problems and needs in the art that havenot yet been fully solved by currently available gas chromatography (GC)sensor technology. Accordingly, the present invention has been developedto provide an apparatus, system, and method for detects chemicalspresent at low concentrations in a GC sensor package that is inexpensiveand simple to manufacture.

A GC sensor is disclosed that includes a first outer sealing body and asecond outer sealing body. The sensor includes a plurality of flowchannels etched into the outer sealing bodies. The sensor includes afirst GC column and a second GC column, both columns between the outersealing bodies. The sensor further includes a valve that switchesbetween a first flow regime and a second flow regime. The first flowregime includes a sample flowing through the first GC column and thenthe second GC column. The second flow regime includes a sample flowingto the second GC column without flowing to the first GC column. Thesensor includes a preconcentration tube, a sampling pump, and a sampleswitching valve. The preconcentration tube includes a preconcentrationmaterial that adsorbs and desorbs chemicals from the sample. The sampleswitching valve switches between a concentration mode and a sensingmode. The concentration mode includes an intake air stream flowingthrough the preconcentration tube in a first direction, and the samplingpump sending a dilute sample through a GC unit that includes the firstand second GC columns. The sensing mode includes the intake air streamflowing through the preconcentration tube in a second direction, and thesampling pump sending the sample through the GC unit.

An apparatus is disclosed for low cost high resolution chemicaldetection. The apparatus includes a plurality of flow channels etchedinto the outer sealing bodies. The apparatus includes a first GC columnand a second GC column, both columns between the outer sealing bodies.The apparatus further includes a valve that switches between a firstflow regime and a second flow regime. The first flow regime includes asample flowing through the first GC column and then the second GCcolumn. The second flow regime includes a sample flowing to the secondGC column without flowing to the first GC column. The apparatus includesa preconcentration tube, a sampling pump, and a sample switching valve.The preconcentration tube includes a preconcentration material thatadsorbs and desorbs chemicals from the sample. The sample switchingvalve switches between a concentration mode and a sensing mode. Theconcentration mode includes an intake air stream flowing through thepreconcentration tube in a first direction, and the sampling pumpsending a dilute sample through a GC unit that includes the first andsecond GC columns. The sensing mode includes the intake air streamflowing through the preconcentration tube in a second direction, and thesampling pump sending the sample through the GC unit.

In one embodiment, the apparatus includes a first pump, a firstresistance, a second resistance, and a third resistance. Each resistancemay be an orifice, a controllable valve, and/or a microboard with poroussubstrate. The first flow regime further includes a first fluid streamfrom the first pump that flows through the first GC column and thesecond GC column, and a second fluid stream directed by the valve thatflows through the second resistance and the first resistance. The secondflow regime further includes a third fluid stream from the first pumpthat flows through the first GC column and the first resistance, and afourth fluid stream directed by the valve that flows through the thirdresistance and the second GC column, wherein the fourth fluid streamfurther prevents the third fluid stream from flowing through the secondGC column.

In one embodiment, the apparatus includes a first resistance, and afourth resistance. The first flow regime further includes a first fluidstream from the first pump that flows through the first GC column andthe second GC column, and a second fluid stream directed by the valvethat flows through the fourth resistance and the first resistance. Thesecond flow regime further includes a third fluid stream from the firstpump that flows through the first GC column and the first resistance,and a fourth fluid stream directed by the valve that flows through thefourth resistance and the second GC column, wherein the fourth fluidstream further prevents the third fluid stream from flowing through thesecond GC column.

In one embodiment, the apparatus includes a first pump, a second pump,and a first resistance. The first flow regime further includes a firstfluid stream from the first pump that flows through the first GC columnand the second GC column, and a second fluid stream directed by thevalve from the second pump that flows through the first resistance,wherein the second stream further prevents the first stream from flowingthrough the first resistance. The second flow regime further comprises athird fluid stream from the first pump that flows through the first GCcolumn and the first resistance, and a fourth fluid stream directed bythe valve from the second pump that flows through the second GC column,wherein the fourth stream further prevents the third stream from flowingthrough the second GC column.

In one embodiment, the apparatus includes a quartz or ceramicimpermeable insert within at least one of the plurality of flowchannels. In one embodiment, the apparatus includes a detector circuitthat detects a target chemical eluting from the first and second GCcolumns, wherein the target chemical occurs in an ambient environment atless than about 1,000 parts-per-billion. The apparatus further includesa preconcentration tube, a sampling pump, and a sample switching valvethat switches between a concentration mode and a sensing mode. Thepreconcentration tube includes a preconcentration material that adsorbsand desorbs chemicals from an intake air stream. The concentration modeincludes flowing the intake air stream through the preconcentration tubein a first direction, and the sampling pump providing a dilute sample toa GC unit comprising the first and second GC columns. The sensing modeincludes flowing the intake air stream through the preconcentration tubein a second direction, and the sampling pump providing a concentratedsample to the GC unit.

The apparatus includes a detector circuit in one embodiment. Thedetector circuit is between the outer sealing bodies, and includes adetector circuit seal. The apparatus includes, in one embodiment, anindependent spring to apply sealing force to enhance the detectorcircuit seal. The apparatus includes a pressure equalizing channelconfigured to equalize pressures between the detector circuit and asample channel.

A method is disclosed for low cost high resolution chemical detection.The method includes providing a first outer sealing body and a secondouter sealing body, etching a plurality of flow channels into the firstsealing body and the second sealing body, and providing a first gaschromatography (GC) column and a second GC column interposed between thefirst and second outer sealing bodies. The method further includesproviding a valve that switches between a first flow regime and a secondflow regime. Operating the valve in the first flow regime includesflowing a sample through the first GC column and then the second GCcolumn. Operating the valve in the second flow regime includes flowingthe sample through the second GC column without flowing the samplethrough the first GC column

In one embodiment, the method includes flowing an intake air streamthrough a preconcentration tube in a first direction to concentratechemicals on the preconcentration tube, and flowing the intake airstream through the preconcentration tube in a second direction todeliver a concentrated sample through a GC unit comprising the first andsecond GC columns. In one embodiment, the method further includesheating the preconcentration tube to a specified temperature, therebyreleasing a known chemical from the preconcentration tube, and detectingelution of the known chemical from the GC unit. The method may includeproviding a detector circuit interposed between the first and secondouter sealing bodies, and providing a detector circuit seal. In oneembodiment, the method includes providing a pressure equalizing channelfrom a sample channel to the detector circuit.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment of the invention. Rather, language referring to thefeatures and advantages is understood to mean that a specific feature,advantage, or characteristic described in connection with an embodimentis included in at least one embodiment of the present invention. Thus,discussion of the features and advantages, and similar language,throughout this specification may, but do not necessarily, refer to thesame embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize that theinvention may be practiced without one or more of the specific featuresor advantages of a particular embodiment. In other instances, additionalfeatures and advantages may be recognized in certain embodiments thatmay not be present in all embodiments of the invention.

These features and advantages of the present invention will become morefully apparent from the following description and appended claims, ormay be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsthat are illustrated in the appended drawings. Understanding that thesedrawings depict only typical embodiments of the invention and are nottherefore to be considered to be limiting of its scope, the inventionwill be described and explained with additional specificity and detailthrough the use of the accompanying drawings, in which:

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem to detect a broad spectrum of chemicals in accordance with thepresent invention;

FIG. 2A is a schematic block diagram illustrating one embodiment of acontroller for a GC sensor in accordance with the present invention;

FIG. 2B is a schematic block diagram illustrating one embodiment of acontroller for a GC sensor in accordance with the present invention;

FIG. 3 is a schematic block diagram illustrating one embodiment of anapparatus to seal a GC sensor and detector circuit in accordance withthe present invention;

FIG. 4 is a schematic block diagram illustrating one embodiment of anapparatus to control flows to GC columns within a GC sensor inaccordance with the present invention;

FIG. 5 is a schematic block diagram illustrating one embodiment of anapparatus to control flows to GC columns within a GC sensor inaccordance with the present invention;

FIG. 6 is a schematic block diagram illustrating an alternativeembodiment of an apparatus to control flows to GC columns within a GCsensor in accordance with the present invention;

FIG. 7 is a schematic block diagram illustrating an alternativeembodiment of an apparatus to control flows to GC columns within a GCsensor in accordance with the present invention;

FIG. 8 is a schematic block diagram illustrating one embodiment of anapparatus to control sampling flows within a GC sensor in accordancewith the present invention;

FIG. 9 is a schematic block diagram illustrating one embodiment of anengineered pressure balancing leak in accordance with the presentinvention;

FIG. 10 is a schematic block diagram illustrating one embodiment of anapparatus to seal a GC sensor and detector circuit in accordance withthe present invention;

FIG. 11 is a schematic block diagram illustrating one embodiment of anapparatus to uniformly heat a GC column in accordance with the presentinvention;

FIG. 12A is a schematic block diagram illustrating one embodiment of aslot for packing a preconcentration material in accordance with thepresent invention;

FIG. 12B is a schematic block diagram illustrating one embodiment of apacked preconcentration material in accordance with the presentinvention;

FIG. 12C is a schematic block diagram illustrating an alternativeembodiment of a packed preconcentration material in accordance with thepresent invention;

FIG. 13 is an illustration of sampling data in accordance with thepresent invention;

FIG. 14 is an illustration of alternative sampling data in accordancewith the present invention;

FIG. 15 is an illustration of sampling data adjusted with a plurality ofnoise wavelets in accordance with the present invention;

FIG. 16 is a schematic flow diagram illustrating one embodiment of amethod to manufacture a GC column in accordance with the presentinvention;

FIG. 17 is a schematic flow diagram illustrating one embodiment of amethod to utilize an internal standard chemical in a GC sensor inaccordance with the present invention;

FIG. 18 is a schematic flow diagram illustrating one embodiment of amethod to pack a preconcentration material in accordance with thepresent invention;

FIG. 19 is a schematic flow diagram illustrating one embodiment of amethod to control the temperature of a GC column in accordance with thepresent invention;

FIG. 20 is a schematic flow diagram illustrating one embodiment of asimilarity sequencing sample data acquisition method in accordance withthe present invention;

FIG. 21 is a schematic flow diagram illustrating one embodiment of amethod for analyzing sampling data in accordance with the presentinvention;

FIG. 22 is a schematic flow diagram illustrating one embodiment of amethod for identifying data peaks and noise peaks in a set of samplingdata in accordance with the present invention; and

FIG. 23 is a schematic flow diagram illustrating one embodiment of amethod for low cost high resolution chemical detection in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the figures herein,may be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the apparatus, system, and method of the presentinvention, as presented in FIGS. 1 through 23, is not intended to limitthe scope of the invention, as claimed, but is merely representative ofselected embodiments of the invention.

Many of the functional units described in this specification have beenlabeled as modules, in order to more particularly emphasize theirimplementation independence. For example, a module may be implemented asa hardware circuit comprising custom VLSI circuits or gate arrays,off-the-shelf semiconductors such as logic chips, transistors, or otherdiscrete components. A module may also be implemented in programmablehardware devices such as field programmable gate arrays, programmablearray logic, programmable logic devices or the like.

Modules may also be implemented in software for execution by varioustypes of processors. An identified module of executable code may, forinstance, comprise one or more physical or logical blocks of computerinstructions which may, for instance, be organized as an object,procedure, or function. Nevertheless, the executables of an identifiedmodule need not be physically located together, but may comprisedisparate instructions stored in different locations which, when joinedlogically together, comprise the module and achieve the stated purposefor the module.

Indeed, a module of executable code may be a single instruction, or manyinstructions, and may even be distributed over several different codesegments, among different programs, and across several memory devices.Similarly, operational data may be identified and illustrated hereinwithin modules, and may be embodied in any suitable form and organizedwithin any suitable type of data structure. The operational data may becollected as a single data set, or may be distributed over differentlocations including over different storage devices, and may exist, atleast partially, merely as electronic signals on a system or network.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, appearancesof the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout this specification are not necessarily all referringto the same embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided, such asexamples of materials, fasteners, sizes, lengths, widths, shapes, etc.,to provide a thorough understanding of embodiments of the invention. Oneskilled in the relevant art will recognize, however, that the inventioncan be practiced without one or more of the specific details, or withother methods, components, materials, etc. In other instances,well-known structures, materials, or operations are not shown ordescribed in detail to avoid obscuring aspects of the invention.

FIG. 1 is a schematic block diagram illustrating one embodiment of asystem 100 to detect a broad spectrum of chemicals in accordance withthe present invention. The system 100 may comprise a gas chromatography(GC) sensor, and a controller 104. The controller may comprise at leastone module configured to control one or more aspects of the GC sensor.The modules in one embodiment may comprise a temperature control module106, a GC column switching module 108, a sample introduction module 110,a similarity sequencing module 112, a signal processing module 114, anda noise-filtering module 116.

The temperature control module 106 may be configured to control thetemperature of one or more GC columns within the GC sensor. Thetemperature control module may be configured to control the temperatureof the GC column(s) based on the current ambient temperature and a setof chemical elution data corresponding to a set of temperatures.

The GC column switching module 108 may be configured to control gasflows through at least one GC column in the GC sensor 102. The GC columnswitching module 108 may be configured to control the flows such that agas flow passes through a first GC column into a second GC column inseries. The GC column switching module 108 may be further configured tocontrol the flows such that a first and second GC column each receive agas flow in parallel. The GC column switching module 108 may be furtherconfigured to ensure that a first and second GC column receivesubstantially the same flow rate of gas.

The sample introduction module 110 maybe configured to introduce asample gas into at least one GC column. The sample introduction module110 may be configured to control a sample flow in a concentration flowregime configured to concentrate a sample gas onto a preconcentrationmaterial, which may be configured to adsorb the sampled chemicals ofinterest. The sample introduction module 110 may be further configuredto control a sample flow in a desorption flow regime to desorb a samplegas from the preconcentration material, and to flow the concentratedsample through the at least one GC column.

The similarity sequencing module 112 may be configured to take datasamples in a constant log-time fashion to ensure that early eluting andlate eluting chemicals exhibit qualitatively similar data peaks. Thesimilarity sequencing module 112 may be configured in one embodiment totake data samples in a constant time fashion, and to process the data tosimulate a constant log-time data set.

The signal processing module 114 may be configured to deconvolute asampling data set to determine the chemical inputs to the at least oneGC column that generate the eluted chemicals observed in the samplingdata. The signal processing module 114 may be configured to deconvolutethe sampling data utilizing a Z-transform. The signal processing module114 may be configured to convert the sequential sampling data into ahigh order polynomial, divide the high order polynomial by a polynomialsystem model, and thereby generate a an input polynomial. The signalprocessing module 114 may be further configured to regenerate thepredicted input signal by an inverse Z-transform of the inputpolynomial. The Z-transform may be modified to use the largestpolynomial divisor possible without generating negative values. Themodified Z-transform may be enabled by the near-constant width in samplespace of the chemical elution peaks generated by the similaritysequencing module 112.

The noise filtering module 116 may be configured to operate a noisesuppression wavelet and/or other noise suppression method on thesampling data to suppress noise peaks. The noise filtering module 116may be further configured to operate a plurality of noise suppressionwavelets on the sampling data, and to identify one or more peaks asnoise, and one or more peaks as data. The noise filtering module 116 maybe configured to identify relatively stable peaks as data, andrelatively unstable peaks as noise.

FIG. 2A is a schematic block diagram illustrating one embodiment of acontroller 104 for a GC sensor 102 in accordance with the presentinvention. The controller 104 may comprise a plurality of modules tofunctionally execute the controller 104 operations.

The controller 104 may comprise a temperature control module 106configured to maintain a GC target temperature 206 at a lowest feasibletemperature to maintain elution time separation of closely relatedchemicals and to minimize the heating burden on the GC sensor 102. Thetemperature control module 106 may be configured to determine an ambienttemperature 202. The temperature control module 106 may be furtherconfigured to read a stored set of temperature-based elution data 204.The temperature control module 106 may then select a GC targettemperature 206 based on the ambient temperature 202 and the set oftemperature-based elution data 204.

In one embodiment, the temperature control module 106 may be configuredto select the next available temperature from the set oftemperature-based elution data 204 higher than the ambient temperature202. In one example, the set of temperature-based elution data 204comprises elution data 204 at 50° F., 100° F., and 150° F. In theexample, the temperature control module 106 may select a GC targettemperature of 100° F. when the ambient temperature 202 is 65° F.

In one embodiment, the temperature control module 106 may be configuredto interpolate elution data between available temperatures in the set oftemperature-based elution data 204, and may be configured to select a GCtarget temperature 206 at any desired temperature. For example, the setof temperature-based elution data 204 may comprise elution data 204 at50° F., 100° F., and 150° F., and the temperature-based elution data 204may be configured to select a GC target temperature 10° F. higher thanthe ambient temperature 202, or 75° F. when the ambient temperature 202is 65° F. The interpolation may be simple interpolation, or wheregreater accuracy is required the interpolation could occur through theapplication of fundamental mass diffusion equations.

The temperature control module 106 may be further configured to providea heating element command 208, which may be a physical control of aheating element, a datalink command to another portion of the controller104 to control the heating element, or the like. The heating element maybe controlled through a standard control scheme such as aproportional-integral-derivative (PID) controller to control the GCcolumn(s) to the GC target temperature 206.

In one embodiment, the set of temperature-based elution data 204contains one set of data for a first GC column, and a second set of datafor a second GC column. The GC target temperature 206 may comprise atarget temperature 206 for each GC column, and the target temperatures206 may be different values for each GC column.

The controller 104 may comprise a GC column switching module 108configured to control gas flows through at least one GC column in the GCsensor 102. The GC column switching module 108 may be configured tocontrol the flows in a first flow regime 210 such that a gas flow passesthrough a first GC column into a second GC column in series. The GCcolumn switching module 108 may be further configured to control theflows in a second flow regime 210 such that a first and second GC columneach receive a gas flow in parallel. The GC column switching module 108may be further configured to ensure that a first and second GC columnreceive substantially the same flow rate of gas.

The GC column switching module 108 may comprise commands to one or morevalves and one or more pumps to achieve the flow regime switches. Thecommands may comprise physical control of the valves and/or pumps, adatalink command to another portion of the controller 104, or the like.

The controller 104 may comprise a sample introduction module 110configured to introduce a sample gas into at least one GC column. Thesample introduction module 110 may be configured to control a sampleflow in a concentration flow regime 212 configured to concentrate asample gas onto a preconcentration material, which may be configured toadsorb the sampled chemicals of interest. The sample introduction module110 may be further configured to control a sample flow in a desorptionflow regime 212 to desorb a sample gas from the preconcentrationmaterial, and to flow the concentrated sample through the at least oneGC column.

The sample introduction module 108 may comprise commands to one or morevalves and one or more pumps to achieve the flow regime switches. Thecommands may comprise physical control of the valves and/or pumps, adatalink command to another portion of the controller 104, or the like.

The controller 104 may comprise a similarity sequencing module 112configured to take data samples in a constant log-time fashion. Earlyeluting chemicals tend to have a sharper peak shape and to elute in ashort period of time. Later eluting chemicals tend to have a flatterpeak shape and to elute over a longer period of time. Therefore, thelater eluting chemicals tend to have a peak created from a much largernumber of samples than earlier eluting peaks, and the different shapesof the peaks tend to make algorithms less likely to detect them. Takingdata in a constant log-time fashion tends to clean up the peaks and makeearly and late eluting chemicals show similar looking peaks. In oneexample, the similarity sequencing module 112 may be configured to takedata samples 214 at each 0.2 log seconds, or the normal time value ofdata point value “n” equals e^n. In the example, data point 12 would be(12*0.2=) log-time 2.4, and the normal time value would be 11.02seconds. Logarithm values other than base “e”, or the natural logarithm,are possible, as the natural logarithm is used only for illustration.

Many applications have a natural data sampling frequency due tocontroller 104 execution times and physical limitations of the sensor102. Therefore, the similarity sequencing module 112 may be configuredin one embodiment to take data samples 214 in a constant time fashion,and to process the data to simulate a constant log-time data set 216.For example, the similarity sequencing module may be configured tophysically collect data each 0.2 seconds. To simulate the 15^(th)log-time data point, the time data from (e^(15*0.2)=) 20.08 seconds to(e^(16*0.2)=) 24.53 seconds would be used. Therefore, the constant timedata points (214) 101-122, as well as part of data point 100, and partof data point 123, would be integrated to simulate the 15^(th) log-timedata point 216.

A rectangular approximation or other integrating algorithm could be usedto integrate the data between the given sample points 214. Simpson'srule, trapezoidal, and polynomial approximations can be used as well,although those integrating algorithms provide little benefit of improvedaccuracy over a rectangular approximation where the constant time datainterval is small, and those algorithms, for example Simpson's rule, mayamplify high frequency signal noise.

The signal processing module 114 may be configured to deconvolute asampling data set 216 to clarify data peaks and find eluted chemicals inthe sampling data. The sampled data set 216 may be affected in time, orconvoluted, due to diffusion and separation in the at least one GC tube.The deconvolution process may recover the original signal, which istypically a chemical concentration in GC sensors 102. The signalprocessing module 114 may be configured to deconvolute the data set 216with the largest polynomial division that does not produce an unstabledata response. The signal processing module 114 may be furtherconfigured to utilize a Z-transform in sampling point space to determinethe input signal according to the following equation where theZ-transform of the system 218 may be a transfer function describing thecharacteristics of the system:

$\begin{matrix}{\frac{Z({output})}{Z({system})} = {{Z({input})}.}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Therefore, the inverse transform of the result of Equation 1 providesthe input data 220 or the information from the sampling data input. AFourier transform can also be used in deriving the data, although theFourier transform is more susceptible to ringing from high frequencynoise.

The signal processing module 114 may be configured to deconvolute thesampling data set to clarify data peaks and find eluted chemicals in thesampling data by converting the sampling data set 216 into a high orderpolynomial, for example by a regression fit. The signal processingmodule 114 may be further configured to interpret a model 218 of the GCcolumn system, which may be a transform function in the formN_(z)/D_(z), or a rational polynomial function. In some embodiments,either Nz or Dz may be 1, reducing the transform function to 1/D_(z) orN_(z), respectively. Those of skill in the art will recognize that ifthe roots of D_(z) fall within the unit circle, the signal convolutionis stable.

The signal processing module 114 may be configured to label the inputchemical sample function as U, the output function as Y, and the systemmodel as G, and to label the Z-transforms of those functions as U_(z),Y_(z), and G_(z). The input function may be convoluted by the GC columnssuch that Y_(z)=G_(z)*U_(z), where Y_(z) is the measured output at thedetector, and U_(z) is the Z-transformed desired input information.Therefore, it is apparent that equation 2 yields the desired inputinformation.Z ⁻¹(Uz)=Z ⁻¹(Yz/Gz)=Z ⁻¹((Yz*Dz)/Nz)   Equation 2.

The signal processing module 114 may be configured to modify theZ-transform division to ensure it is stable. This may be accomplishedwith a standard division configured to avoid a negative result. In thefollowing example, polynomials are expressed as coefficients onlywithout the related powers (e.g. X²+2X+3=[1 2 3]). In one example, N_(z)may be [3 2 1 2 3 2 1] while D_(z) may be [1 1 1]. The first factor tocheck may be 3/1=3, generating a first intermediate result of (3-3*12-3*1 1-3*1 2 3 2 1), or (0 −1 −2 2 3 2 1) with the result being (1).Note that the result contains negative values, and is thereforeunstable. The second intermediate result is (0 0 −4 0 3 2 1) with theresult being (1 −1). The next becomes (0 0 0 −4 −1 2 1) result=(1 −1−4). The result is beginning to exhibit fluctuations.

Continuing the analysis by testing factors under the restriction of nonegative results, it is apparent that the first factor for the exampleshould be 1. With 1 the result will be (2 1 0 2 3 2 1). As there are nonegative values this is acceptable. Proceeding to the next factor, 1 isselected. This also produces negative values so it is reduced to 0. Thesecond result would be (2 1 0 2 3 2 1) with the result being (1 0). Thethird is (2 1 0 2 3 2 1) with the result (1 0 0), The fourth is (2 1 0 01 0 1) and (1 0 0 2). Continuing to the end yields (2 1 0 0 1 0 1) and(1 0 0 2 0 0 0).

The signal processing module 114 may be configured to complete thedeconvolution under equation 2. The modified Z-transform takes care ofany instability introduced by any problematic zeros. Note that themodified z transform method makes an implicit assumption that allfeatures of interest convolute similarly as the divisor is constant. Ifthe divisor is not constant, for example because the width of peaks ofinterest increases at later elute times then further modification may beutilized. A first modification is to change the divisor for each timeperiod of interest. This is within the skill of one in the art, but maynot be the preferable solution in some circumstances. A secondmodification is to adjust the time sampling such that the peaks havesimilar features and the constant divisor remains valid. The similaritysequencing module 112 may be configured to perform the secondmodification. In embodiments utilizing a Fourier transform or otherdeconvolution methods, the divisor issue remains and the modificationslisted may still be utilized in some embodiments.

The noise filtering module 116 may be configured to operate a pluralityof noise suppression wavelets 222 and/or other noise suppression methodson the sampling data, and to identify one or more peaks as noise, andone or more peaks as data. Each noise suppression methodology may makeassumptions about the noise shape. These assumptions are known as thenoise model. Changing the noise model will affect the result of thenoise suppression step, which will introduce or eliminate differentnoise generated artifacts in the results.

The noise filtering module 116 maybe further configured to identifyrelatively stable peaks as data, and relatively unstable peaks as noise.A stable peak in this context is a peak that is present even whenseveral noise suppression methods are used. An unstable peak is onewhose presence is dependent on the noise model used and thus is notpresent in some of the responses. The noise filtering module 116 may beconfigured to operate a noise suppression wavelet 222 or other noisesuppression method on the sampling data to suppress noise peaks. Thenoise filtering module 116 may be further configured to operate aplurality of noise suppression wavelets 222 on the sampling data, and toidentify one or more peaks as noise 224, and one or more peaks as data224. The noise filtering module 116 may be configured to identifyrelatively stable peaks as data, and relatively unstable peaks as noise

In one embodiment, the noise filtering module 116 may be configured tooperate a set number of noise filtering wavelets 222 on the samplingdata at each time step, and to identify peaks 224 which remainsubstantially constant as data, and peaks 224 which move orintermittently appear as noise. Substantially constant may comprise arange of amplitudes and a range of time values wherein a peak can appearand still be considered to be the same peak. Moving or intermittentlyappearing may comprise values outside of the range of amplitudes and therange of time values wherein a peak can appear and still be consideredto be the same peak.

In one embodiment, the noise filtering module 116 may be configured witha larger number of noise suppression wavelets 222 than the noisefiltering module 116 may run on each execution time step. In oneexample, the noise filtering module 116 may comprise ten noisesuppression wavelets 222, and the noise filtering module 116 may operatethree noise suppression wavelets 222 at each time step. The three noisesuppression wavelets may comprise a random selection from the tenavailable wavelets 222, a rotation within the ten available wavelets222, or a primary noise suppression wavelet 222 and two waveletsselected from the other nine available wavelets 222. This embodimentavoids having a noise suppression wavelet 222 that may be sensitive insome operating conditions dominate the signal, while improving theoperational performance of the controller 104 compared to running allwavelets 222 at every execution cycle.

FIG. 2B is a schematic block diagram illustrating one embodiment of acontroller 104 for a GC sensor 102 in accordance with the presentinvention. In the embodiment of FIG. 2B, the apparatus includes apreconcentration tube (refer to the sections referencing FIGS. 4 through8B) having a preconcentration material that adsorbs and desorbschemicals from an intake air stream. The preconcentration material, inone embodiment, releases a known chemical at a specified temperature226. The GC sensor 102 includes an internal standard delivery module 228that heats the preconcentration material to the specified temperature226.

The internal standard delivery module 228 may heat the preconcentrationmaterial by issuing a heat preconcentration command 230 to an actuatorsuch as a resistive heater, and/or similar method known in the art. Theinternal standard delivery module 228 may be configured to heat thepreconcentration material on a maintenance schedule, upon a request,upon the detection of a GC sensor fault 102, and the like. Upon heatingto the specified temperature 226, the preconcentration material createsa known chemical release 232, which a calibration module 234 isconfigured to detect. The calibration module 234 detects elution of theknown chemical from a GC unit comprising a first and second GC column(refer to the description referencing FIGS. 8A and 8B, for example), andprovides known chemical elution data 236. The system 100 may beconfigured to utilize the known chemical elution data 236 to providedynamic information about the system (e.g. a system transfer function),to determine a sensor 102 fault condition, and the like.

FIG. 3 is a schematic block diagram illustrating one embodiment of anapparatus 300 to seal a GC sensor 102 and detector circuit 316 inaccordance with the present invention. The apparatus 300 may comprise afirst sealing surface 304 configured to seal the sensor 102 from anambient environment. The first sealing surface 304 may be an epoxy orsimilar sealant configured to seal the material of the sensor 102 bodywhich may comprise a machineable ceramic. In one embodiment, an acrylicGP sealant is used at the sealing surface 304. The apparatus 300 mayfurther comprise a second sealing surface 306 configured to seal adetector circuit 316 from internal leaks within the sensor 102.

The first sealing surface 304 may seal the faces of a first outersealing body and a second outer sealing body, wherein the outer sealingbodies together comprise the body of the sensor 102. Refer to thedescription referencing FIG. 10.

The apparatus may further comprise a GC unit 308 which may comprise atleast one GC column, and a sample unit 310 configured to provide thesample gas to the sensor 102 and GC unit 308. The sample may pass fromthe GC unit 308 to the detector 316. The detector 316 may comprise anydetection device used in the GC art—including a thermal conductivitydetector (TCD), a mass spectrometer, flame ionization detector,photo-ionization detector, electron capture detector, Hall electrolyticconductivity detector, and the like. In one embodiment, the detector 316comprises a TCD, and the detector 316 is configured to generate anelectrical signal based on the detected thermal conductivity of thesample gas on one side of a Wheatstone bridge, with an electrical signalbased on the detected thermal conductivity of a reference gas on theother side of the Wheatstone bridge. This known compensation techniqueremoves common mode noise, or background noise, from the signal andfocuses the detection on the sample 310 gas.

The apparatus 300 may comprise a controller 104, which may communicatewith the detector 316, an ambient temperature sensor 312, and a GC unittemperature sensor 314. The temperature control module 106 may beconfigured to utilize the temperature sensors 312, 314 to control thetemperature of the GC column(s) within the GC unit 308.

Regarding FIGS. 4 through 8B, embodiments with two different switchingschemes are described. The first switching scheme is designed toimplement the switching between two GC columns GC1, GC2, and embodimentsof this scheme are described in FIGS. 4 through 7. The second switchingscheme is used to load and unload sampled chemicals on apreconcentration tube 402, and to alternate sample air and clean air tothe inlet of GC1. One embodiment of the second switching scheme isdetailed in FIGS. 8A and 8B. A given embodiment of the invention maycomprise either or both switching schemes. They are illustratedseparately to clarify the features of the invention, and it is amechanical step for one of skill in the art to combine embodiments ofthe first and second switching schemes in a given embodiment of theinvention.

FIG. 4 is a schematic block diagram illustrating one embodiment of anapparatus 400 to control flows to GC columns within a GC sensor 102 inaccordance with the present invention. FIGS. 4 through 8B use thestandard convention that where a flow depends upon the position of avalve, a dashed line indicates that the given flow is not occurring withthe valve in the position as shown within that Figure. The apparatus 400may comprise a first GC column GC1, a second GC column GC 2, and aplurality of flow resistances (restrictions) R1, R2, R3. The first andsecond GC columns GC1, GC2 are interposed between the first and secondouter sealing bodies. The GC columns may be disposed within a cavitymachined or cast into the sealing bodies.

The flow resistances R1, R2, R3 may comprise orifices, controllablevalves, inserted microboard with porous substrate, or any other type ofconfigurable pressure drop available in the art. In one embodiment, theflow resistances comprise flow channels sized to achieve a specifiedpressure drop at a specified flow rate. The flow channels of theapparatus 400 may be etched on the surfaces of opposing faces of thesensor 102 body, or they may be machined flow paths within a sensor 102body.

The apparatus 400 may comprise a preconcentration tube 402, a pump 404,and a molecular sieve 406. The molecular sieve 406 may be configured toremove water and/or other impurities from the gas flow in the apparatus400, and may be affixed between the pump 404 inlet and outlet. Theapparatus 400 shows only the relative flows of GC1 and GC2, while otherflows into and out of the apparatus 400 are not shown to avoidcluttering the essential aspects of the embodiment of the invention.Significantly, the introduction of sample 310 gas into the system is notshown. Sample 310 gas may be introduced at the pump 404 through themolecular sieve, for example.

The apparatus may further comprise a valve 408 configured to direct flowthrough resistance R2 or resistance R3. The valve 408 may comprise asolenoid valve. In FIG. 4, the valve 408 is directing flow throughresistance R2. The flow through R2 carries the flow out of GC1 into GC2,thereby connecting the GC columns in series, and sending the output ofGC1 and GC2 into the detector 316. The detector 316 effluent may vent tothe atmosphere 410. In one embodiment, a majority of the flow through R2may flow through R1 and recycle through the pump 404.

FIG. 4 illustrates the valve 408 set to the first flow regime. In theembodiment of FIG. 4, a first fluid stream 412 from the pump 408 flowsthrough the first GC column GC1 and the second GC column GC2. A secondfluid stream 414 directed by the valve 408 flows through the secondresistance R2 and the first resistance R1.

The depiction in FIG. 4 thereby describes a valve 408 that switchesbetween a first flow regime (as depicted in FIG. 4) and a second flowregime (as depicted in FIG. 5). The flow channels depicted in FIGS. 4through 8B are etched into the first sealing body and the second sealingbody such that when the sealing bodies are placed together, sealed flowchannels are thereby created. The first flow regime comprises a sample(starting at the pump 404) flowing through the first GC column GC1 andthen the second GC column GC2. The second flow regime (refer to FIG. 5)comprises a sample (starting at the pump 404) flowing through the secondGC column GC2 without flowing through the first GC column GC1.

Referring to FIG. 5, the valve 408 is directing flow through restrictionR3. The flow through R3 forces the flow from GC1 away from GC2, andthrough R1 for venting or recycling. The flow through GC2 is provided bythe pump 404. It is apparent from FIGS. 4 and 5 that the apparatus 400is configured to direct gas flows through the GC columns GC1, GC2 inseries or parallel with the use of a solenoid valve 408.

FIG. 5 illustrates the valve 408 set to the second flow regime. In theembodiment of FIG. 5, a third fluid stream 502 from the pump 408 flowsthrough the first GC column GC1 and the first resistance R1. A fourthfluid stream 504 directed by the valve flows through the thirdresistance R3 and the second GC column GC2. The fourth fluid stream 504further prevents the third fluid stream 502 from flowing through thesecond GC column GC2.

FIG. 6 is a schematic block diagram illustrating an alternativeembodiment of an apparatus 600 to control flows to GC columns GC1, GC2within a GC sensor 102 in accordance with the present invention.Referring to FIGS. 4 and 5, it is apparent that for the flow ratesthrough GC1 and GC2 to be identical in either position of the valve 408,a condition which may be desirable for the detector 316, the flowrestrictions R2, R3 must be identical. Referring back to FIG. 6, thoseflow restrictions may be replaced with a single restriction R4 beforethe valve 408 which enforces this condition more effectively. Theembodiment of FIG. 6 is otherwise identical to the embodiment of FIG. 5.

The embodiment of FIG. 6 thus depicts a first flow regime comprising afirst fluid stream from the pump 408 that flows through the first GCcolumn GC1 and the second GC column GC2, and a second fluid streamdirected by the valve 408 that flows through the fourth resistance R4and the first resistance R1. The valve 408 in FIG. 6 is depicted in theposition to induce the first flow regime. FIG. 6 further depicts asecond flow regime comprising a third fluid stream from the pump 408that flows through the first GC column GC1 and the first resistance R1,and a fourth fluid stream directed by the valve 408 that flows throughthe fourth resistance R4 and the second GC column GC2. The fourth fluidstream further prevents the third fluid stream from flowing through thesecond GC column GC2. The valve 408 would be turned—similar to theembodiment depicted in FIG. 5—to induce the second flow regime.

FIG. 7 is a schematic block diagram illustrating an alternativeembodiment of an apparatus 700 to control flows to GC columns GC1, GC2within a GC sensor 102 in accordance with the present invention.Referring to FIG. 6, it is apparent that for the flow rates through GC1and GC2 to be identical in either position of the valve 408, the flowrestriction R4 must dominate the observed pressure drops for flowthroughout the apparatus 600. Referring back to FIG. 7, the single pump404 is replaced with two pumps 702, 706 which may comprise correspondingmolecular sieves 704, 708.

The two pumps 702, 706 may enforce the flow rates through GC1 and GC2 tobe identical because the pump 607 controls the flow rate through GC1,and the pump 702 can control the flow rate through GC2. The controller104 may be configured to control the pumps 702, 704. The restriction R4may be removed in the apparatus 700, although it may be included (notshown), or lumped with R1 to place the restriction on the low pressureside of the pump 702 instead of the high pressure side if desired. Theremoval of the restriction R4 may cause a lower nominal pressure in theanalysis flowpaths of the sensor 102, and thereby increase thesensitivity of the GC sensor 102 to leaks. It is within the skill of onein the art to weigh the increased manufacturing costs to manage leaks, ahigher pressure load on the pump 702, and a loss in sensor 102measurement capability due to unmanaged leaks when determining theinclusion of the restriction R4.

Thus, FIG. 7 depicts an embodiment comprising a first pump 706 and asecond pump 702. In the embodiment of FIG. 7, a first flow regimecomprises a first fluid stream from the first pump 702 that flowsthrough the first GC column GC1 and the second GC column GC2. The firstflow regime further includes a second fluid stream directed by the valve408 from the second pump 702 that flows through the first resistance R1.The second stream further prevents the first stream from flowing throughthe first resistance R1. The valve 408 in FIG. 7 is positioned to inducethe first flow regime.

FIG. 7 further depicts a second flow regime comprising a third fluidstream from the first pump 706 that flows through the first GC columnGC1 and the first resistance R1, and a fourth fluid stream directed bythe valve 408 from the second pump 702 that flows through the second GCcolumn GC2. The fourth stream further prevents the third stream fromflowing through the second GC column GC2. The valve 408 would beturned—similar to the embodiment of FIG. 5—to induce the second flowregime. In the embodiment of FIG. 7, sample may be introduced at thefirst pump 706.

FIG. 8A is a schematic block diagram illustrating one embodiment of anapparatus 800 to control sampling flows within a GC sensor 102 inaccordance with the present invention. The flow channels of theapparatus 800 may be etched on the surfaces of opposing faces of thesensor 102 body, or they may be machined flow paths within a sensor 102body. In one embodiment, the flow channels may comprise ceramic orquartz inserts in the analytical (i.e. sample-containing) portions ofthe sensor 102 to further enhance sealing of the sensor 102 and allowlower concentrations of chemicals in the sample 310 to be detected. Suchinserts are estimated to allow detections down into theparts-per-billion (ppb) range—for example below about 1,000 ppb. Theapparatus 800 may comprise a valve 804 configured to operate theapparatus 800 in the concentration or desorption modes. The apparatus800 of FIG. 8 is shown in the concentration mode. Some of the valves andflow paths similar to those depicted in FIGS. 4 through 7 are removedfrom FIG. 8 to avoid obscuring aspects of the present invention.However, in one embodiment, FIG. 8 retains the pump(s) 404, 702, 706,and valve 404 to allow flow through the GC columns GC1, GC2 in seriesand/or parallel as shown in FIGS. 4 through 7.

In the embodiment of FIG. 8A, the sample 310 is introduced to thepreconcentration tube 402 which may adsorb the chemicals of interest. Apump 806 may send gas through a carrier gas flow restriction R6 and tothe GC unit 308. Some of the pump 806 effluent may recycle through adesorption flow restriction R7 and return to the pump 806 through thevalve 804. The flow may pass from the GC unit 308 to the detector 316,where it may flow through a system flow restriction R5 and to anatmospheric vent 808 or back to the pump 806. Therefore, in oneembodiment of the concentration mode, the preconcentration tube 402 isconcentrating the sample gas, and the GC unit 308 is receiving cleanambient or carrier gas.

In one embodiment, FIG. 8A depicts a preconcentration tube 402, asampling pump 806, and a sample switching valve 804. The sampleswitching valve 804 switches between a concentration mode and a sensingmode. The embodiment of FIG. 8A depicts the valve 804 in theconcentration mode. The concentration mode comprises an intake airstream 810 flowing through the preconcentration tube 402 in a firstdirection (e.g. left to right in FIG. 8A), and the sampling pump 806sending a dilute sample 812 through a GC unit 308 comprising the firstand second GC columns GC1, GC2.

Referring to FIG. 8B, an embodiment is illustrated with the apparatus800 in the desorption flow regime. The valve 804 is directing flow fromthe pump 806 reversed through the preconcentration tube 402. Note thatthe valve 804 has shut down the flow from the pump 806 through thecarrier flow restriction to the GC unit 308, although the physicalconnection of the valve 304 to that flow channel is not shown in FIG. 8Bto prevent cluttering the Figure. The sample 310 gas flows through atube shunt flow restriction R9 to the valve 804 and through thepreconcentration tube 402, while the pump 806 flow that went to the GCunit 308 is redirected to the valve 804 through a sample flowrestriction R8. Therefore, in one embodiment of the desorption mode, thepreconcentration tube 402 is desorbing sample gas to the GC unit 308.

In one embodiment, FIG. 8B depicts the valve 804 in the sensing mode.The sensing mode comprises an intake air stream 814 flowing through thepreconcentration tube 402 in a second direction (right to left in FIG.8B), and the sampling pump 806 sending a concentrated sample 816 throughthe GC unit 308.

FIG. 9 is a schematic block diagram illustrating one embodiment of anengineered pressure equalizing channel 902 in accordance with thepresent invention. The detector circuit seal 306 protects the detector316 from intruding gases which may ruin the sample from the GC unit 308.In one embodiment, the detector seal 306 is considerably more effectiveif the detector 316 circuit is at an equal pressure with sample 310channel. If a pressure equalizing channel 902 is engineered between thesample 310 flow path and the detector 316, equalizing a first pressurein the sample channel with a second pressure in the detector 316circuit. In one embodiment, the pressure equalizing channel 902 isengineered in parallel along the sample channel, from the sample 310introduction through the GC unit 308.

FIG. 10 is a schematic block diagram illustrating one embodiment of anapparatus 1000 to seal a GC sensor 102 and detector circuit 316 inaccordance with the present invention. The sensor seal 304 may comprisean adhesive between faces of a first outer sealing body 1008 and asecond outer sealing body 1010 of the sensor 102 body. The faces of thefirst outer sealing body 1008 and the second outer sealing body 1010 maybe pressed together by a plurality of fasteners 1004 with a pressuremaintenance mechanism such as a plurality of lock washers 1006.

The detector circuit 316 may be within a cavity in the sensor 102, andmay have a sealing surface 306 which may comprise an adhesive betweenthe surfaces 306. The detector seal may further comprise a pressuremechanism 1002 independent from the pressure mechanism 1006 of thesensor seal 304. The pressure mechanism 1002 may comprise one or moresprings configured to apply pressure to the detector circuit 316 faces306 to keep them sealed.

The sealing surface 306 may include a pressure equalizing channel 902.In one embodiment, the apparatus 1000 includes at least one spring 1002interposed between the first and second outer sealing bodies 1008, 1010,wherein the spring(s) 1002 apply force to enhance the detector circuit316 seal.

FIG. 11 is a schematic block diagram illustrating one embodiment of anapparatus 1100 to uniformly heat a GC column GC1 in accordance with thepresent invention. The apparatus 1100 may comprise a heating element1102. The heating element 1102 may comprise a heating element 1102 witha higher wattage rating than the required wattage to heat the GC columnGC1 from the lowest predicted ambient temperature 202 to the highest GCtarget temperature 206. Such a design allows the heating element 1102 toprovide the heat required for the sensor at a lower current and heatingelement 1102 temperature than a minimally specified heating elementwould. Such a design minimizes the potential for heat spikes andnon-uniformity throughout the GC column GC1.

The apparatus 1100 may further comprise insulation 1104 between theheating element and the GC column GC1. The insulation 1104 furtherreduces the occurrence of temperature variability induced in the GCcolumn GC1 by the heating element 1102.

FIG. 12A is a schematic block diagram illustrating one embodiment 1200of slot 1204 machined into the sensor body 1202 for packing apreconcentration material in accordance with the present invention. Theslot 1204 may be machined vertically into the sensor body 1202 and theapparatus 1200 may be packed vertically. Further, the slot 1204 maycomprise a slot machined into the sensor body 1202, with a tube insertedinto the slot, wherein the apparatus 1200 is packed into the tube.

Referring to FIG. 12B, the slot may be packed by inserting a slurrycomprising microspheres and adhesive to form a uniformly porous plug1206 at a first end of the slot 1204, and packing in thepreconcentration material 1208. The apparatus 1200 may be completed byinserting a slurry to form a uniformly porous plug 1206 at a second endof the slot 1204. Referring to FIG. 12C, it may be desirable to offsetthe preconcentration material 1208 from the adhesive slurry 1206.Therefore, the apparatus 1200 of FIG. 12C shows the preconcentrationmaterial 1208 separated from the adhesive slurry 1206 by a pair ofoffset rods 1210 configured to offset the preconcentration material 1208the desired distance.

The adhesive slurry may comprise glass microspheres. The adhesive maycomprise an epoxy glue comprising 10% or less by weight of the slurry.The glass-glue mixture provides a consistent pressure drop once evenlymixed.

FIG. 13 is an illustration of sampling data 1300 shown in constant time,in accordance with the present invention. The example data labeled Chem1 may be a typical elution peak for a relatively fast-eluting chemical,and the example data labeled Chem 2 may be a typical elution peak for arelatively slow-eluting chemical. Note that the time scale for FIG. 13is relative only, and that the differences between the fast-eluting andslow-eluting chemicals are compressed to demonstrate the similarityeffect and relative peak shapes. In practice, chemicals with elutionpeak widths that vary as much as those shown in FIG. 13 will often, butnot necessarily, exhibit much greater separation in the time axis.

The fast eluting chemical may comprise a sharp peak as shown, and arelatively small number of sample points. The slow eluting chemical maycomprise a flattened peak as shown, and a relatively large number ofsample points. The area under the peaks is similar in the examples, asevidenced by the similar final values of the integration curves,indicating that these two chemicals were in the sample at approximatelythe same concentrations. The differences in the peak widths and thenumber of samples in each peak may complicate the use of a modifiedZ-transform in analyzing GC sensor 102 signals.

FIG. 14 is an illustration of sampling data 1400 shown in constant logtime, in accordance with the present invention. For purposes ofillustration, the same example data from FIG. 13 is shown in FIG. 14,and therefore the time axis differences between the fast and sloweluting chemicals may likewise be compressed in FIG. 14. The fasteluting chemical may comprise a sharp peak as shown. The slow elutingchemical may comprise a similarly shaped peak in constant log time. Thepeaks for the fast and slow eluting chemicals in FIG. 14 may exhibitsimilar numbers of sample points within each peak. Note that theintegral curves in FIG. 14 are generated with a rectangular estimate,and that close observation of the integral curves in FIG. 14 illustratesthat although the fast and slow eluting chemicals had the same areaunder the curve in constant time sampling, they are not at exactly thesame area under the curve in constant log-time sampling, although theintroduced error is small.

FIG. 15 is an illustration of sampling data adjusted with a plurality ofnoise suppression methods in accordance with the present invention. Thefirst data set 1502 may show a data set adjusted by a first noisesuppression method, the second data set 1504 may show a data setadjusted by a second noise suppression method, and the third data set1506 may show a data set adjusted by a third noise suppression method.In one embodiment, the noise-filtering module 116 may label a peak atabout 15 time units as data because this peak occurs in all three sets1502, 1504, 1506. The noise-filtering module 116 may label peaks atabout 45, 65, 75, 90, and 130 time units as noise because these peaksappear on only some of the sets 1502, 1504, 1506. Further, thenoise-filtering module 116 may label a peak at about 115 time units asdata because this peak occurs in all three data sets 1502, 1504, 1506.The noise suppression methods may be noise suppression wavelets.

The schematic flow chart diagrams included herein are generally setforth as logical flow chart diagrams. As such, the depicted order andlabeled steps are indicative of one embodiment of the presented method.Other steps and methods may be conceived that are equivalent infunction, logic, or effect to one or more steps, or portions thereof, ofthe illustrated method. Additionally, the format and symbols employedare provided to explain the logical steps of the method and areunderstood not to limit the scope of the method. Although various arrowtypes and line types may be employed in the flow chart diagrams, theyare understood not to limit the scope of the corresponding method.Indeed, some arrows or other connectors may be used to indicate only thelogical flow of the method. For instance, an arrow may indicate awaiting or monitoring period of unspecified duration between enumeratedsteps of the depicted method. Additionally, the order in which aparticular method occurs may or may not strictly adhere to the order ofthe corresponding steps shown.

FIG. 16 is a schematic flow diagram illustrating one embodiment of amethod 1600 to manufacture a GC column GC1, GC2 in accordance with thepresent invention. The method 1600 may be performed with a torsionspring making machine configured to manage materials of the diameter ofthe GC column GC1, GC2. The method 1600 may begin with bending 1602 atube of slightly longer than the desired GC column length into a GCcolumn GC1, GC2. Then, the tube may be crimped 1604 at the ends tofacilitate maintaining tube cleanliness during storage 1606 and/ortransport 1606 of the column GC1, GC2. Then method 1600 may continuewith a practitioner cutting 1608 off the ends of the column GC1, GC2 andinstalling 1610 the column GC1, GC2 into a GC sensor 102.

FIG. 17 is a schematic flow diagram illustrating one embodiment of amethod 1700 to utilize an internal standard chemical in a GC sensor 102in accordance with the present invention. The method 1700 may begin withpacking 1702 a preconcentration material 1208 into a GC sensor. Thepreconcentration material 1208 may comprise a known material, forexample Tenax, that releases a known byproduct at a set temperature. Themethod 1700 may proceed with heating 1704 the preconcentration material1208 to a specified temperature at which the known byproduct isreleased. The controller 104 may then track 1706 the elution of theknown byproduct, and compare 1708 the elution time to a known standardelution time according to the temperature of the GC columns GC1, GC2.

FIG. 18 is a schematic flow diagram illustrating one embodiment of amethod 1800 to pack a preconcentration material 1208 in accordance withthe present invention. The method 1800 may begin with a practitionermixing 1802 a microsphere-adhesive slurry and placing 1804 some of theslurry at one end of a slot 1204. The practioner may then insert 1806 anoffset rod into the slot to position a preconcentration material in theslot 1204. The practitioner may then pack 1808 a preconcentrationmaterial into the slot, and insert 1810 another offset rod into theslot. The practitioner may then fill the slot 1204 withmicrosphere-adhesive slurry to complete the packing of thepreconcentration material.

FIG. 19 is a schematic flow diagram illustrating one embodiment of amethod 1900 to control the temperature of a GC column GC1, GC2 inaccordance with the present invention. The method 1900 may begin 1902with the controller storing 1902 a set of elution versus temperaturedata for a number of chemicals of interest. The temperature controlmodule 106 may be configured to detect 1904 the ambient temperature 202,and to select 1906 a target temperature 206 for the GC column(s) basedon the ambient temperature 202 and the elution versus temperature data204. The temperature control module 106 may be further configured toheat 1908 the GC column(s) GC1, GC2 to the target temperature 206.

FIG. 20 is a schematic flow diagram illustrating one embodiment of asimilarity sequencing sample data acquisition method 2000 in accordancewith the present invention. The method 2000 may begin with thesimilarity sequencing module 112 determining 2002 whether a variabletime step sampling rate is available. Where variable time step samplingis available, the similarity sequencing module 112 may collect 2004 datain a constant log-time step, wherein each data point proceeds at thetime value t, where:t=A*e ^(k*s)   Equation 3.

In Equation 2, s is the sample number to be taken, and t is the normaltime at which the sample is taken. The value k determines the distancebetween sample increments, while the value A is used to define the timeat which the first sample is taken. For example, the value k may be 0.2,and A may be 1. In the example, the first sample is taken atapproximately 1.22 seconds, the second sample at 1.49 seconds, andanother sample is taken at each 0.2 log-seconds. In the example, the20^(th) sample would be taken at about 54.6 seconds.

Where variable time step sampling is not available, the similaritysequencing module 112 may collect 2010 data in a constant normal-timestep, and process 2012 the data to simulate constant log-time steps.

The method 2000 may proceed with the similarity sequencing module 112storing 2006 the sample data, and the controller 104 may make 2008 thestored data available to a signal processing algorithm on the signalprocessing module 114.

FIG. 21 is a schematic flow diagram illustrating one embodiment of amethod 2100 for analyzing sampling data in accordance with the presentinvention. The method 2100 may begin with the signal processing module114 receiving 2102 sample data 216 which may be sequenced by thesimilarity sequencing module 112. The signal processing module 114 mayreceive 2104 a system characterization which may comprise a Z-transformtransfer function of the system 100. The signal processing module 114may deconvolute 2106 the sample data 216 with the largest polynomialdivision that does not produce a negative response and induceinstability. The signal processing module 114 may then determine theinput signal according to Equation 2.

FIG. 22 is a schematic flow diagram illustrating one embodiment of amethod 2200 for identifying data peaks and noise peaks in a set ofsampling data 216 in accordance with the present invention. The method2200 may begin with the noise filtering module 116 receiving sample data216. The noise filtering module 116 may then apply 2204 a plurality ofnoise suppression wavelets 222 to the sample data 216. The noisefiltering module 116 may then generate 2206 a set of data peaks, andidentify 2208 shifting peaks as noise, and stable peaks as signal ordata.

FIG. 23 is a schematic flow diagram illustrating one embodiment of amethod 2300 for low cost high resolution chemical detection inaccordance with the present invention. Some steps of the method 2300 maybe implemented by a controller 104. The method 2300 includes providing2302 a first outer sealing body 1008 and a second outer sealing body1010. The method 2300 further includes etching 2304 a plurality of flowchannels into the first outer sealing body 1008 and a second outersealing body 1010. The method 2300 continues with providing 2306 a firstGC column GC1 and a second GC column GC2 and further providing 2308 avalve 408 that switches between a first flow regime and a second flowregime. The method 2300 includes operating 2310 the valve in the firstflow regime by flowing a sample through the first and second GC columnsGC1, GC2, and operating 2312 the valve in the second flow regime byflowing a sample through the second GC column GC2 without flowing thesample through the first GC column GC1.

The method 2300 further includes flowing 2314 an intake air streamthrough a preconcentration tube 402 in a first direction to concentratechemicals on the tube 402, and flowing 2316 the intake air streamthrough the preconcentration tube 402 in a second direction to deliver aconcentrated sample to a GC unit 308. The method 2300 may furtherinclude heating 2318 the preconcentration tube 402 to a specifiedtemperature, thereby releasing a known chemical from preconcentrationmaterial in the preconcentration tube 402, and detecting elution of theknown chemical from the GC unit 308. The method 2300 may further includeproviding a detector circuit 316 interposed between the first and secondouter bodies 1008, 1010, providing a detector circuit seal, and furtherproviding a pressure equalizing channel from a sample channel to thedetector circuit 316.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An apparatus for high resolution chemical detection, comprising: afirst outer sealing body and a second outer sealing body; a plurality offlow channels etched into the first outer sealing body and the secondouter sealing body; a first gas chromatography (GC) column and a secondGC column interposed between the first and second outer sealing bodies;and a valve that switches between a first flow regime and a second flowregime, wherein the first flow regime comprises a sample flowing throughthe first GC column then the second GC column, and wherein the secondflow regime comprises the sample flowing to the second GC column withoutflowing through the first GC column.
 2. The apparatus of claim 1,wherein the valve is a solenoid valve.
 3. The apparatus of claim 1,further comprising a first pump, a first resistance, a secondresistance, and a third resistance, wherein: the first flow regimefurther comprises a first fluid stream from the first pump that flowsthrough the first GC column and the second GC column, and a second fluidstream directed by the valve that flows through the second resistanceand the first resistance; and the second flow regime further comprises athird fluid stream from the first pump that flows through the first GCcolumn and the first resistance, and a fourth fluid stream directed bythe valve that flows through the third resistance and the second GCcolumn, wherein the fourth fluid stream further prevents the third fluidstream from flowing through the second GC column.
 4. The apparatus ofclaim 1, further comprising a first pump and a second pump, and a firstresistance, wherein: the first flow regime further comprises a firstfluid stream from the first pump that flows through the first GC columnand the second GC column, and a second fluid stream directed by thevalve from the second pump that flows through the first resistance,wherein the second stream further prevents the first stream from flowingthrough the first resistance; and the second flow regime furthercomprises a third fluid stream from the first pump that flows throughthe first GC column and the first resistance, and a fourth fluid streamdirected by the valve from the second pump that flows through the secondGC column, wherein the fourth stream further prevents the third streamfrom flowing through the second GC column.
 5. The apparatus of claim 1,further comprising a first pump, a first resistance, and a fourthresistance, wherein: the first flow regime further comprises a firstfluid stream from the first pump that flows through the first GC columnand the second GC column, and a second fluid stream directed by thevalve that flows through the fourth resistance and the first resistance;and the second flow regime further comprises a third fluid stream fromthe first pump that flows through the first GC column and the firstresistance, and a fourth fluid stream directed by the valve that flowsthrough the fourth resistance and the second GC column, wherein thefourth fluid stream further prevents the third fluid stream from flowingthrough the second GC column.
 6. The apparatus of claim 5, wherein eachresistance comprises a flow resistor selected from the flow resistorsconsisting of an orifice, a controllable valve, and a microboard withporous substrate.
 7. The apparatus of claim 1, wherein at least one ofthe plurality of flow channels further comprises an impermeable insertinterposed between the first and second outer sealing bodies.
 8. Theapparatus of claim 7, wherein the impermeable insert comprises one of aquartz insert and a ceramic insert.
 9. The apparatus of claim 8, furthercomprising a detector circuit that detects a target chemical elutingfrom the first and second GC columns, wherein the target chemical occursin an ambient environment at less than about 1,000 parts-per-billion.10. The apparatus of claim 1, further comprising a preconcentrationtube, a sampling pump, and a sample switching valve, wherein: thepreconcentration tube comprises a preconcentration material that adsorbsand desorbs chemicals from an intake air stream; and the sampleswitching valve switches between a concentration mode and sensing mode,wherein the concentration mode comprises the intake air stream flowingthrough the preconcentration tube in a first direction, and a thesampling pump sending a dilute sample through a GC unit comprising thefirst and second GC columns, and wherein the sensing mode comprises theintake air stream flowing through the preconcentration tube in a seconddirection, and the sampling pump sending a concentrated sample throughthe GC unit.
 11. The apparatus of claim 10, wherein the preconcentrationmaterial releases a known chemical at a specified temperature, theapparatus further comprising an internal standard delivery moduleconfigured to heat the preconcentration material to the specifiedtemperature, and a calibration module configured to detect elution ofthe known chemical from the GC unit.
 12. The apparatus of claim 11,wherein the preconcentration material comprises an adsorbent resin. 13.The apparatus of claim 1, further comprising a detector circuitinterposed between the first and second outer sealing bodies, whereinthe detector circuit comprises a detector circuit seal, and wherein theapparatus further comprises a pressure equalizing channel configured toequalize a first pressure in a sample channel with a second pressure inthe detector circuit.
 14. The apparatus of claim 13, further comprisingat least one spring interposed between the first and second outersealing bodies, wherein the at least one spring applies force to enhancethe detector circuit seal.
 15. A method for high resolution chemicaldetection, comprising: providing a first outer sealing body and a secondouter sealing body; etching a plurality of flow channels into the firstouter sealing body and the second sealing body; providing a first gaschromatography (GC) column and a second GC column interposed between thefirst and second outer sealing bodies; providing a valve that switchesbetween a first flow regime and a second flow regime; operating thevalve in the first flow regime by flowing a sample through the first GCcolumn and then the second GC column; and operating the valve in thesecond flow regime by flowing the sample through the second GC columnwithout flowing the sample through the first GC column.
 16. The methodof claim 15, further comprising flowing an intake air stream through apreconcentration tube in a first direction to concentrate chemicals onthe preconcentration tube, and flowing the intake air stream through thepreconcentration tube in a second direction to deliver a concentratedsample through a GC unit comprising the first and second GC columns. 17.The method of claim 16, further comprising heating the preconcentrationtube to a specified temperature thereby releasing a known chemical fromthe preconcentration tube, and detecting elution of the known chemicalfrom the GC unit.
 18. The method of claim 15, further comprisingproviding a detector circuit interposed between the first and secondouter sealing bodies, and providing a detector circuit seal.
 19. Themethod of claim 18, further comprising providing a pressure equalizingchannel from a sample channel to the detector circuit.
 20. Agas-chromatography sensor comprising: a first outer sealing body and asecond outer sealing body; a plurality of flow channels etched into thefirst outer sealing body and the second outer sealing body; a first gaschromatography (GC) column and a second GC column interposed between thefirst and second outer sealing bodies; a valve that switches between afirst flow regime and a second flow regime, wherein the first flowregime comprises a sample flowing through the first GC column then thesecond GC column, and wherein the second flow regime comprises thesample flowing to the second GC column without flowing through the firstGC column; and a preconcentration tube, a sampling pump, and a sampleswitching valve, wherein: the preconcentration tube comprises apreconcentration material that adsorbs and desorbs chemicals from anintake air stream; and the sample switching valve switches between aconcentration mode and sensing mode, wherein the concentration modecomprises the intake air stream flowing through the reconcentration tubein a first direction, and the sampling pump sending a dilute samplethrough a GC unit comprising the first and second GC columns, andwherein the sensing mode comprises the intake air stream flowing throughthe preconcentration tube in a second direction, and the sampling pumpsending a concentrated sample through the GC unit.